There is conventionally known an electrophotographic type image forming apparatus including a toner box accommodating toner therein, and a developing device positioned upward of the toner box and provided with a photosensitive drum.
In this image forming apparatus, the toner box is formed with a supply opening at an intermediate portion thereof in an axial direction of the photosensitive drum, and return openings each being formed at each end portion of the toner box in the axial direction. Toner accommodated in the toner box is supplied to the developing device through the supply opening. Toner that has been supplied into the developing device is conveyed in the axial direction by an auger provided in the developing device, and is returned into the toner box through the return openings. Toner supplied to the developing device is supplied by a supply roller to a developing roller positioned upward of the supply roller while the toner is conveyed in the axial direction, and then, the toner supplied to the developing roller is supplied to the photosensitive drum positioned upward of the developing roller.